Often, semiconductor devices include one or more reference voltage sources and/or one or more reference current sources. The semiconductor devices can be analog circuits, digital circuits, or mixed signal analog and digital circuits. Each of the semiconductor devices can be a single integrated circuit chip or multiple integrated circuit chips. Reference voltage sources and reference current sources are two of the major building blocks of analog circuits, such as radio frequency (RF) circuits.
Sometimes, reference voltage sources and reference current sources include a bandgap reference circuit that includes two diodes running at different current densities. The voltage difference between the two diodes is used to generate a proportional to absolute temperature (PTAT) current in a first resistor. The PTAT current is used to generate a voltage in a second resistor, which is added to the voltage of one of the diodes or a third diode. The voltage across a diode operated at a constant current or at the PTAT current is complementary to absolute temperature (CTAT), i.e., reduces with increasing temperature at approximately −2 mV/K. If the ratio between the first and second resistor is chosen properly, the first order effects of the CTAT dependency of the diode and the PTAT current cancel and the resulting voltage is about 1.2-1.3 V, which is close to the theoretical bandgap of silicon at 0 K. The voltage change over operating temperature is on the order of a few millivolts and has a parabolic behavior.
Typically, one or more reference currents are generated in an analog circuit. The reference currents can be generated via a bandgap reference and one or more resistors. The bandgap reference voltage can be maintained across the resistors to provide the reference current. Resistance values of the resistors are subject to process variations, such as doping levels in the silicon, which results in changes in the reference current. The changes in the reference current due to process variations can be more than three times the changes in bandgap voltage due to process variations.
For these and other reasons there is a need for the present invention.